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DynaFlite Super Decathlon Kit Bash and Build

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DynaFlite Super Decathlon Kit Bash and Build

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Old 05-03-2013, 08:16 AM
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mattnew
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Default DynaFlite Super Decathlon Kit Bash and Build

Goals:
Build a good flying dynaflite decathlon.
Try some different construction techniques and hopefully learn a thing or two.
Reduce the flying weight of the plane from ~16-18lbs as most appear to be to around ~13-14lbs, having it balance with a GT33 in the nose and hopefully not much else in the way of lead weight
Have some fun.


Motivation:
Things I hear about this kit; great flyer, heavy, with a G38 in the nose you have to add nose weight to balance it... hmmmm

The more I looked over the plans, and the more I looked at other planes in my stable, the more I became convinced I could cut just about half the wood out of the tail and body and still have a solidly constructed plane.

examples:
The decathlon uses 3/8" x 15/16" sticks to build up the majority of the tail and parts of the body.
RC extras 30% extra 230; tail is constructed using primarily 3/8" square sticks
1/4 scale clipped wing cup; 3/8' x 1/2" sticks along with some 1/4" square sticks from what I can tell through the covering
1/3 fly baby; 3/8' square, some 3/8"x1/2", mostly spruce however
Nosen Citabria; 3/8" square, some 3/8"x1/2", mostly spruce

My point here would seem to be that this tail, for what the plane is would seem to be a bit massively overbuilt. if an extra 230 doesn't need 15/16" thick sticks to build, I can't imagine a decathlon would etc....

Without trying to go for a homerun and make the lightest possible decathlon, what I'm going to do is make what I feel are "prudent decisions and design changes that should add lightness without impacting the structural integrity of the plane.


step 1, build the elevators. We will keep the spruce spar and use it to attach the flying wires to, however all 15/16" wood is gone, substituting in 3/8" x 1/2". I cut down the 6" wide center section to 3" as well and reconfigured the stringers so there are now 6 1/8" x 3/8" stringers instead of the plans which show 4 I think this is still overkill...






We are trying something new for me with glues as well. No CA on this plane, any glue used will either be Titebond, 30 minute epoxy, and possibly some ambroid. In an effort to use less glue, I've found that the testors glue tips fit perfectly on Target's syringes that we get with some of the meds... so once the kiddo's are don'e being sick with there colds.. the syringes end up in my hobby shop. so far I've liked how they work, quite a bit less mess than using hte big bottle.







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Old 05-03-2013, 09:33 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Its still a tank....I probably have half the wood that the original design calls for and its still solid as a rock, I probably could have used 3/8" square here instead of the 3/8" x 1/2". You can see on the plans I was fiddling around with adding the diagonal spars to strengthen this... but its not going to be needed, just added weight.




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Old 05-05-2013, 03:48 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

The rest turned out much lighter, andI'm much happier with the weight of the individual elevators. Need to get a scale to weigh them, but same thing again though, substituting 1/2" wide where the plans call for 15/16", basically cutting hte amount of wood used there in half.



I thought of cutting back on the laminations around the curved lines, however most of this gets sanded away anyway.



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Old 05-07-2013, 10:00 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

6.4 oz for the elevator on its own.

The O.S. GT33 weighs ~43.85 oz according to O.S.'s website, so I'm building using that as a target. For the Decathlon, the ratio of length between the engine to the CG vs the tail section to the CG is roughly 3:1, or the tail is 3x longer moment than the moment to the engine. That means for every ounce out on the tail, 3 ounces near the engine will balance it.

so. 43.85 oz / 3 = 14.61 oz = very rough target weight for tail to balance engine.

so obviously, the body between the tail and engine will contribute to this, the gas tank/cowl/prop hinges covering tailwheel, main wheels etc will all add to this equation, but for rough numbers this seems like a decent starting point. I'll be a happy man if the elevator and rudder come in at or around 10 oz.


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Old 05-07-2013, 10:18 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Looking good!

there is one in my club, built per plans, flies very well, cant remember what engine he used, I think its a G26.

Bill S.
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Old 05-08-2013, 08:49 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Thanks Bill,

The default build for the plane per instructions is done either around the G26 or the US engines 25cc engine, i can't remember which. Both nearly identical magneto based engines that weigh close to 60oz, or just shy of 4lbs. With this engine, I believe most have had to add nose weight to get the plane to balance, and since I'm going with an engine that is 20oz lighter, I'm more than a little concerned that I'll be adding lbs back to the nose to make the plane balance out.

By the way, I'm very open to discussion and constructive feedback on better ways to do this plane so that I am able to meet some of my targets. Like I said , hoping to learn a thing or two here.
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Old 05-08-2013, 12:18 PM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build


ORIGINAL: mattnew

Thanks Bill,

The default build for the plane per instructions is done either around the G26 or the US engines 25cc engine, i can't remember which. Both nearly identical magneto based engines that weigh close to 60oz, or just shy of 4lbs. With this engine, I believe most have had to add nose weight to get the plane to balance, and since I'm going with an engine that is 20oz lighter, I'm more than a little concerned that I'll be adding lbs back to the nose to make the plane balance out.

By the way, I'm very open to discussion and constructive feedback on better ways to do this plane so that I am able to meet some of my targets. Like I said , hoping to learn a thing or two here.
I built mine with a G38 up front. The plans allow some flexibility as to servo mount locations, I placed mine aft of the cabin, leaving a substantial space in the cabin for future detailing, should that be desired. Even so, I added another 4 oz of weight back by the aft servo hatch for best flight response. Adding noseweight to this design really puzzles me. I can't imagine doing that with a G38. I covered with SIG Koverall and painted with latex paint. The plane did not fly "heavy".

If I were to do it again, I would move the firewall back somewhat, as the stock design is overly long in the nose, presumably to facilitate balance with a lighter engine.

Good luck with your build.

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Old 05-09-2013, 06:51 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Thanks for the info, I think your numbers make sense with what I've been reading/researching, The G38 weighs 11oz more than the G26, so if you had put a G26 in you would have needed 7oz in the nose to obtain the same balance as you had with the G38 + 4oz weight in the tail.

I'm looking forward to flying this plane....

I need to get some more build pics up here.
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Old 05-09-2013, 06:58 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

ignoring the 3:1 ratio...the rear servos are much closer to the cabin,
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Old 05-09-2013, 02:07 PM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Mine has a G38 also, no extra balance weight needed, Came in at 17 lbs, Flies very well.
ED
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Old 05-11-2013, 04:32 PM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

nothing revolutionary with the rudder. I struggled a bit with deciding how, if i modified the rudder, would the rudder still attach securely to the plane. since I didn't have the fuselage built yet, testing anything was out of the question and the plans weren't the greatest for showing how the tail end of the fuselage and the rudder joined together. Ah well. We went with the lightest wood that we had and modifed the top of it a little bit, but nothing crazy....







tail weight..... 9.9oz, still some sanding and shaping to do here, however I usually save final sanding to the end.





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Old 05-11-2013, 06:34 PM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Hi Matt, Since you and I are building at the same time, I'll go weigh my tail feathers and give you the "per plans" weight for comparison. I am 60% complete on the fuse. I did modify the wing mounting design to use a wing tube. This meant I changed the shape of the fuse. I have some pics if you're interested.
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Old 05-12-2013, 07:57 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Thanks Red, I'd be interested to see if I saved anything here. Like I said above, much of this is just a learning exercise since I know the stock plane is such a good flyer.

Do you have a thread going on what you did to change the fuselage? would love to see some details.

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Old 05-12-2013, 10:08 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Well Matt, I was sure shocked by what I found! My tail feathers as built weighed in at 9.6oz! That's 0.3 oz LESS that your reduced tail. I didn't do anything different than the plans - EXCEPT I added the hard points for the tail wire mounting.
I wonder if your wood was just really heavy?

I can't upload pics for some silly reason. I keep getting an "Internal Server Error"
My Horizontal Stab/elevators weigh in at 6.2 oz. The Vert Stab/Rudder at 3.4 oz. Weighed together, obviously 9.6 Oz.
Once I can get photos uploaded, I'll send a pic of the Fuselage mod for the Wing Tube design.
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Old 05-12-2013, 03:21 PM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

ha!
was it hinged? I do have 0.3oz of robart super hinges in there.

I've been getting some really heavy wood lately... its really been a bit disappointing. The decathlon kit is mostly very dense balsa. I recently finished an RV-4 that consisted of some of the heaviest balsa I've ever built with. And for the changes I made here I ordered wood from National Balsa and received what I'd basically call concrete. I went to my local LHS and grabbed a few pieces but for the most part my thinking was that with the amount of wood I was cutting out I should be well under stock weight.

I'm fairly confident had I used the stock wood in my kit I would have come in at close to 20 oz. I had weighed the pieces separately rough cut and was already around 17.5 oz. 


hmmm.....
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Old 05-13-2013, 04:48 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Subscribed.. looking good so far.
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Old 05-13-2013, 01:46 PM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Sorry that I didn't get back this sooner, but have been away from the keyboard most of the weekend. I have a Dynaflite Decathlon that I've been working on and off again for awhile now. I have it framed up ready to sand. Anyway, I'll try to get in and weigh my tail feathers tonight. I built them strictly stock by the plans, so I'll let you know what they come out to.

Ken
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Old 05-15-2013, 08:04 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Can't wait to see your numbers as well Ken.

I'm about 75% through the first wing now.. will post some more pictures shortly.


One thing I'm liking about the glue... is while it slows you down, it doesn't really slow the build down that much. I'm taking my time more and getting better joints first... rather than just throwing pieces together and whacking down some superglue. Much more pleased with my final results.

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Old 05-15-2013, 09:46 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Sorry, I got lazy the other night when I got home. I saw the tail feathers hanging on the wall as I headed out to work this morning and thought "Shoot, I forgot to weigh those!!!"  

I'll try to get them tonight when I get home.

Ken
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Old 05-15-2013, 09:48 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build


ORIGINAL: mattnew

One thing I'm liking about the glue... is while it slows you down, it doesn't really slow the build down that much. I'm taking my time more and getting better joints first... rather than just throwing pieces together and whacking down some superglue. Much more pleased with my final results.
I gave up on using CA's in my building long ago, and now I use wood glue like you are using (Carpenter's Wood Glue). I feel that my building improved when I went to wood glue, for a few different reasons. But you couldn't get me to go back to using CA if you paid me to do it. I like the results I get from the wood glue.

Ken

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Old 05-15-2013, 05:57 PM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Matthew, very clean build.  I've a Super Decathlon in a box so this build is very interesting to me.  (I've got thirty kits in boxes so picking a priority isn't as easy as it might be.)   I also like good looking plane and this is a handsome plane.  Follow with interest.  Cliffc

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Old 05-15-2013, 06:52 PM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Very nice joints!
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Old 05-16-2013, 05:48 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Its the glue!

ok its not the glue... but using the wood glue definitely has slown me down and made me more patient. I noticed with CA I tended to get very slappity slappity with parts... make em fit close enough them dump some glue on, if it stuck it must be good enough. With the titebond doesn't matter how fast I slap things together I still have to wait 30 minutes for the glue to set so it has really helped me get things bumped up a notch in terms of quality.

regardless of the eternal fight over which glue is better, I'm apparently a better builder with the wood glue than with the CA. I won't get rid of CAcompletely.... just not for the majority of the plane.

ORIGINAL: KitBuilder

Very nice joints!
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Old 05-17-2013, 07:05 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build


Progress on the wing. everything is stock here... the wood for the wing was decent quality and the build was pretty standard... I haven't found much worth trying to change yet....



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Old 05-19-2013, 11:31 AM
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Default RE: DynaFlite Super Decathlon Kit Bash and Build

Sorry that it took me so long to get the numbers on the weight for my tail feathers. I built them straight off the plans. The only modifications I did was to install Robart Hinge Points for my hinges. The weight of the vertical stabilizer, rudder, horizontal stabilizer, elevators, and all the hinges was 9.125 oz. This weight is before I have sanded the surfaces.

Hope this helps

Ken
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